They all appear to have been given the same explanation in a cover letter - that it was due to an increased risk of stormwater run-off.

Still, Mrs Fretus, who has lived in their Warilla home for 53 years, didn't think the 800 per cent increase could possibly be right.

"We thought it was a mistake and we went to the office at Shellharbour and she said 'no, that's not a mistake, that's right'," Mrs Fretus said.

"But she said 'if you want to ring the main office, you can'. So we did and they said the same thing."

So the Fretuses took their business elsewhere, to an insurer that charges about $6000 less a year - an insurer who clearly does not believe that the Fretuses' home is anywhere near the risk that NRMA does.

It was a similar situation for David Durber in Hewitts Ave, Thirroul. His NRMA home and contents premium climbed from about $1000 to $7941.

"I was just horrified. I thought, 'are these people for real?"' Mr Durber said.

"I rang them up and they said that this information has been provided to us as a result of hydrologists' reports and other information supplied by council and these increases were the result of it."

Mr Durber has lived in the house for 16 years and, even in the terrible floods of 1998, he said the water came no further than his back garden.

He too has jumped ship to a different insurer.

"They're charging more or less around the rate that we were charged with NRMA last year," he said.

Those customers with years of loyalty to NRMA still faced a sudden spike in this year's premium.

Robert Clayton of Sunnybank Crescent, Horsley, said he had his home and contents insured with NRMA for more than 30 years.

This year he found his premium had risen by more than $2600 - and he said that was taking into account discounts for being a long-time customer, having linked policies and a no-claim bonus.

A spokesman from NRMA Insurance said that the Fretus and Durber properties were considered "to have a high level of risk to stormwater run-off".

"We take into account factors such as where the property is located on a block, the height of the land and whether a home is elevated," the spokesman said.

"We also take into account their proximity to stormwater canals, drains and channels. Different properties within a suburb will have different levels of risk."

Have you been affected? Email scoop@illawarramercury.com.au or phone 4221 2206.